Monocytic cells (e.g., macrophages) play critical roles as accessory cells, proinflammatory cells and destructive effector cells both in septic and in non-septic (e.g., arthritis, hypersensitivity) inflammatory reactions and are the predominant cell type present in such lesions. Although cytokines secreted by activated T cells play many roles in enhancing and inhibiting macrophage function, it has become apparent that contact-dependent signaling during T cell- macrophage conjugate formation plays a critical role in activation of macrophage function, as evidenced by the reduced capacity of CD40- ligand deficient T cells to induce macrophage inflammatory activity. Recent studies have revealed reduced T cell and B cell function in aged animals. However, there have been few studies on macrophage function and those have been limited to examination of macrophage responses to bacterial endotoxin. We propose to examine the effect of senescence on T cell contact-dependent signaling of macrophages. The study will encompass both CD40-dependent and CD40-independent contact signaling of macrophages from old (24 month) and young (2 month) mice by T cells from young and old mice to distinguish deficient responses caused by reduced T cell signaling versus reduced macrophage responsiveness. Since aging may differentially affect macrophages from different tissue sources, resident peritoneal macrophage, bone marrow-derived macrophages, and spleen-derived macrophages will be compared. The study will determine if decreased function is due to decreased T cell function and/or decreased macrophage responsiveness to T cell signaling. Intracellular signaling (total and activated protein tyrosine kinase, MAPK activation) by CD40-dependent and independent pathways will be assayed. Macrophage functions to be examined include production of inflammatory (IL-1, TNFalpha) and anti-inflammatory (IL-10, TGFbeta) cytokines, IL-12, chemokines (MCP-1, MIP-1), and generation of nitric oxide and superoxide.